quinta-feira, 9 de junho de 2011
White-nose syndrome of Bats: An enemy in the cave
Scientists who study bats have unwittingly become detectives on the trail of a troubling mystery.
It began during the winter of 2006. A visitor exploring a cave near Albany, N.Y., photographed hibernating bats. He noted they looked odd, because their noses were covered in strange, white fuzz — a lot like the fuzz on a moldy peach.
The following winter, other people began noticing disturbing signs at nearby caves: Bats were flying around aimlessly in broad daylight, probably in search of food. Normally the bats would be roosting (nestled closely together) in place all winter.
Then, in March 2007, researchers came upon a scene straight out of a nightmare. They stumbled onto thousands of bat skeletons scattered across the floor of one of the caves. The previous spring, bats here had been plump, healthy and thriving.
In short order, biologists would find this ghoulish scene at caves and mines throughout the Northeastern United States. And always there was the mysterious white fuzz clinging to the bats’ ears, wings and muzzles.
Its spread was rapid. By 2010, the scourge had reached Canada to the north and as far south as Tennessee.
This sickness, called white-nose syndrome (WNS), is now creeping westward. It has leapfrogged to caves and mines 800 miles from its original site. Indiana was recently confirmed to have WNS, and the disease is suspected to have reached as far south and west as Oklahoma.
At least six of the 45 species of bats in North America have been hit with white nose — including the little brown bat and the endangered Indiana bat (also found outside the state). Scientists estimate that more than a million bats have died, and perhaps far more than that.
The apparent culprit is a fungus known as Geomyces destructans. Unlike the fungus that thrives on sweaty feet and causes athlete’s foot, this one prefers chilly, moist spots like the caves and abandoned mines where bats hibernate. Researchers don’t quite understand why the fungus makes bats sick, but scientists are racing to gather as many clues as possible to try and thwart the disease. Their best hope is to slow the spread of the disease between caves and across the country. Ultimately, scientists are working to prevent mass extinctions of bats — or their permanent loss.
Bats are “not charismatic, they’re not big and furry, but they are beautiful little animals,” says Hazel Barton, a cave microbiologist at Northern Kentucky University in Highland Heights. But she thinks it’s hard for many people to care about bats’ survival “because they don’t realize how important of a role [bats] play.”
Bats disperse seeds and pollinate flowers. They recycle key nutrients, pooping out natural fertilizers that benefit soils and cave ecosystems. And they provide critical environmental services to people by eating insects responsible for many crop and forest diseases.
A single hibernation site can be home to anywhere from dozens to hundreds of thousands of bats. In some instances, 100 to 150 bats may squish into an area the size of a Frisbee. Bats sometimes hang side by side, forming thick, furry carpets on the walls and ceilings of caves and mines. When researchers spot the telltale fuzz on hibernating bats, they know the animals’ future is grim. In sites where bats are afflicted with WNS, up to 99 percent (or, 99 in 100) of the bats will likely die.
“We call them zombies because they’re going to be dead by the end of the season,” says Barton. “It feels like death is there visiting.”
Since WNS arrived, the lives of bat researchers have been tough. The worst is when you go back to caves where healthy bats had lived year after year, says Gregory Turner. He’s an endangered-mammal specialist with the Pennsylvania Game Commission.
In one Pennsylvania cave, researchers had come to recognize a tiny tricolored bat that hung onto the same rusty nail all winter long for at least 15 years. But in 2010, this bat went missing. And it wasn’t just that bat that went missing. Of some 2,800 bats that once lived in the cave, the researchers found only 35 that season.
So far, WNS seems to be affecting only hibernating bats. Researchers suspect this may provide an important clue to how the fungus gets a foothold.
During hibernation, bats breathe just a few times an hour. Their metabolism, or energy production, drops into slow motion. And their immune systems, which fight infection and illness, are on pause. “They’re just sort of in cold storage,” says DeeAnn Reeder, a bat biologist at Bucknell University in Lewisburg, Penn. “Normally that works just fine for them.” But then “along comes this cold-loving fungus that happens to grow best when the animals have no immune competence.”
Healthy bats emerge from hibernation for only about an hour or two — something called an arousal — once every two weeks. Researchers believe that bats with WNS may be arousing from hibernation too frequently. Each time bats arouse, they have to rev up their metabolism, sort of like warming up a car or rebooting a computer. This process burns precious fat reserves that the bats need to get through the winter. As a result, bats become unusually hungry, and the search for food may be why they leave their caves early. But during the winter, they find few insects. This repeated disturbance depletes their energy reserves. And over time, scientists now believe, this causes the bats to starve to death. They may be too thin to reproduce when spring arrives.
The fungus also erodes the bats’ wings, turning them into something resembling cheesecloth, thin and with small holes. So bats that make it through the winter may still be unable to fly well enough to catch food.
“There are probably multiple things happening that are having a domino effect,” says Reeder. “We’re just trying to figure out what all those dominoes are and how they all relate.”
Scientists aren’t sure how G. destructans got here. It may have hitched a ride to the United States from Europe, probably on the clothes or shoes of someone who went into a cave. Indeed, the fungus appears identical to a fungus that lives in Europe. But bats in Europe so far appear to be healthy. And that makes researchers suspect that European bats may have developed a resistance to the fungus long ago.
American bats represent a New World (Western Hemisphere) population, says Barton, and the fungus constitutes an Old World (European) disease. Its arrival in the United States is probably much like when European settlers arrived in America, bringing smallpox. Native Americans had never been exposed to smallpox, which turned out to be very deadly to them.
“I don’t think there’s any difference between what happened then and what we’re seeing with the bats,” Barton says. “The New World population had no resistance, it had never been exposed to the organism before, and as a result there was high mortality.”
White-nose syndrome highlights how little we know about germs like bacteria and fungi, says David Blehert, a microbiologist (someone who studies tiny organisms) with the United States Geological Survey’s National Wildlife Health Center in Madison, Wis. While it’s rare for scientists to discover new species of mammals or birds, he explains that “the microbial world is still 99 percent unknown to science.”
“Caves that bats hibernate in are just absolutely full of brothers and sisters and cousins of this fungus that are very closely related — but yet somehow different,” Blehert adds. “Understanding those differences will be key to understanding why this one [microbe] is so bad.”
Researchers do not yet understand how white nose spreads. But if they can’t learn how to stop it in its tracks, it could prove catastrophic for farmers and forest managers.
In summer and early fall, bats gorge on insects. A female bat can eat 4,500 insects in a single night, or more than 100 percent of her body weight. “That’s like me going out and having 500 quarter-pounders every night,” says Reeder. Bats feast on hoards of insects in order to store up fat for the winter.
Experts estimate that the loss of one million bats represents 700,000 tons of uneaten insects each summer. So “hundreds and hundreds of tractor trailers full of insects that would have been taken out by the bats” are now sticking around, says Barton. Many of these are agricultural pests, such as moths, that munch on food crops and cotton. To cope with the loss of bats, farmers may feel forced to use more pesticides, which would lead to an increase in air and water pollution.
Researchers are working feverishly, but so far have identified no way to stop the spread of white nose. “The efforts right now to find something to treat the bats or to prevent the fungus from growing are more of a Band-Aid than a cure,” says Turner.
Stalking the enemy
At a handful of sites, researchers are attempting to kill the fungus by scattering a variety of natural chemical compounds in winter-hibernating bat colonies. But preliminary data suggest that the treatment may be toxic to the bats too. And because bats live in complex ecosystems, researchers must also think about other beneficial organisms that could be affected by the treatment.
“We could spray the bats with an antifungal that might kill the white nose, but then it might kill everything else in the cave that the bats need to survive for the long term,” says James Eggers. He directs conservation programs at Bat Conservation International, based in Austin, Texas. “We want to find something that can specifically target this one fungus and not cause damage to other essential fungi.”
One way that researchers study hibernating bats without disturbing them is by gluing tiny data loggers that resemble M&M’s onto the bats’ backs. The loggers record the temperature of the bats’ skin and tell researchers how often the bats are arousing from hibernation.
Bat biologists suspect that bats living in colder hibernating colonies might have an advantage over those in slightly warmer ones. So, in a handful of sites, researchers hope to experiment with creating microclimates (steady climate conditions in a small area) by altering temperature and humidity. This approach might be effective in certain states, such as Pennsylvania, where 90 percent of bats hibernate inside abandoned mines. (It would be inappropriate for researchers to modify the climate of caves, which contain very complex natural ecosystems.)
“There are days that I feel like we’re doing everything we can and we’re just documenting an extinction,” says Reeder. Still, she sees room for hope.
“The only thing I know how to do is stick my nose to the grindstone and just work,” she says. “Hopefully, somewhere in that process we can come up with some information that will allow us to stop this [disease] and understand what’s going on.”
Power words (adapted from Yahoo! Kids dictionary):
arouse: The brief time when animals emerge from sleep or hibernation. Bats occasionally emerge from hibernation and bring their body temperature up to about 100 degrees Fahrenheit for one or two hours. Then the bats drop back into hibernation, and their bodies return to the surrounding temperature, usually about 45° F.
ecosystem: The organisms and environmental elements (such as rocks and soil) of a shared area.
fungus: Any of many organisms in the kingdom Fungi. They lack chlorophyll (used in photosynthesis) and vascular tissue (like blood in animals and sap in plants) and range in form from a single cell to a body mass of branched, threadlike structures. The kingdom includes yeasts, molds, smuts and mushrooms.
hibernate: To be temporarily inactive, or dormant, usually during the winter.
microclimate: The climate of a small, specific place within an area as compared with the climate of a broad region.
pollinate: The transfer of pollen (a powdery material used in flowering plant reproduction) from an anther (the male part of a flower) to the stigma (the female part of a flower).
roost: A place to temporarily rest or sleep.
speleology: The scientific study or exploration of caves.